1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17/*
18 * Functions for interpreting LEB128 (little endian base 128) values
19 */
20
21#ifndef LIBDEX_LEB128_H_
22#define LIBDEX_LEB128_H_
23
24#include "DexFile.h"
25
26/*
27 * Reads an unsigned LEB128 value, updating the given pointer to point
28 * just past the end of the read value. This function tolerates
29 * non-zero high-order bits in the fifth encoded byte.
30 */
31DEX_INLINE int readUnsignedLeb128(const u1** pStream) {
32    const u1* ptr = *pStream;
33    int result = *(ptr++);
34
35    if (result > 0x7f) {
36        int cur = *(ptr++);
37        result = (result & 0x7f) | ((cur & 0x7f) << 7);
38        if (cur > 0x7f) {
39            cur = *(ptr++);
40            result |= (cur & 0x7f) << 14;
41            if (cur > 0x7f) {
42                cur = *(ptr++);
43                result |= (cur & 0x7f) << 21;
44                if (cur > 0x7f) {
45                    /*
46                     * Note: We don't check to see if cur is out of
47                     * range here, meaning we tolerate garbage in the
48                     * high four-order bits.
49                     */
50                    cur = *(ptr++);
51                    result |= cur << 28;
52                }
53            }
54        }
55    }
56
57    *pStream = ptr;
58    return result;
59}
60
61/*
62 * Reads a signed LEB128 value, updating the given pointer to point
63 * just past the end of the read value. This function tolerates
64 * non-zero high-order bits in the fifth encoded byte.
65 */
66DEX_INLINE int readSignedLeb128(const u1** pStream) {
67    const u1* ptr = *pStream;
68    int result = *(ptr++);
69
70    if (result <= 0x7f) {
71        result = (result << 25) >> 25;
72    } else {
73        int cur = *(ptr++);
74        result = (result & 0x7f) | ((cur & 0x7f) << 7);
75        if (cur <= 0x7f) {
76            result = (result << 18) >> 18;
77        } else {
78            cur = *(ptr++);
79            result |= (cur & 0x7f) << 14;
80            if (cur <= 0x7f) {
81                result = (result << 11) >> 11;
82            } else {
83                cur = *(ptr++);
84                result |= (cur & 0x7f) << 21;
85                if (cur <= 0x7f) {
86                    result = (result << 4) >> 4;
87                } else {
88                    /*
89                     * Note: We don't check to see if cur is out of
90                     * range here, meaning we tolerate garbage in the
91                     * high four-order bits.
92                     */
93                    cur = *(ptr++);
94                    result |= cur << 28;
95                }
96            }
97        }
98    }
99
100    *pStream = ptr;
101    return result;
102}
103
104/*
105 * Reads an unsigned LEB128 value, updating the given pointer to point
106 * just past the end of the read value and also indicating whether the
107 * value was syntactically valid. The only syntactically *invalid*
108 * values are ones that are five bytes long where the final byte has
109 * any but the low-order four bits set. Additionally, if the limit is
110 * passed as non-NULL and bytes would need to be read past the limit,
111 * then the read is considered invalid.
112 */
113int readAndVerifyUnsignedLeb128(const u1** pStream, const u1* limit,
114        bool* okay);
115
116/*
117 * Reads a signed LEB128 value, updating the given pointer to point
118 * just past the end of the read value and also indicating whether the
119 * value was syntactically valid. The only syntactically *invalid*
120 * values are ones that are five bytes long where the final byte has
121 * any but the low-order four bits set. Additionally, if the limit is
122 * passed as non-NULL and bytes would need to be read past the limit,
123 * then the read is considered invalid.
124 */
125int readAndVerifySignedLeb128(const u1** pStream, const u1* limit, bool* okay);
126
127
128/*
129 * Writes a 32-bit value in unsigned ULEB128 format.
130 *
131 * Returns the updated pointer.
132 */
133DEX_INLINE u1* writeUnsignedLeb128(u1* ptr, u4 data)
134{
135    while (true) {
136        u1 out = data & 0x7f;
137        if (out != data) {
138            *ptr++ = out | 0x80;
139            data >>= 7;
140        } else {
141            *ptr++ = out;
142            break;
143        }
144    }
145
146    return ptr;
147}
148
149/*
150 * Returns the number of bytes needed to encode "val" in ULEB128 form.
151 */
152DEX_INLINE int unsignedLeb128Size(u4 data)
153{
154    int count = 0;
155
156    do {
157        data >>= 7;
158        count++;
159    } while (data != 0);
160
161    return count;
162}
163
164#endif
165